1. Field of the Invention
This invention relates to improvements in the use of dielectric heating in the production of food products. More specifically, this invention relates to the use of dielectric heating in close proximity to a food extruder to significantly accelerate the drying of the extruded food product.
2. Description of the Background Art
Dielectric heating has been used in a wide variety of industries since the 1930's when dielectric heating was utilized by the tobacco industry to dry tobacco. Since then, dielectric heating has been utilized in the ceramics, paper, food, oil, leather and glass industries for purposes as diverse as plastic pre-heating, wood gluing, cork heating, sterilization and foundry core baking.
In the food industry, dielectric heating has long been used in combination with conventional ovens for cookie and cracker drying. U.S. Pat. No. 3,082,710 to Holland, describes a process and apparatus for baking biscuits with a combination of conventional heating and dielectric heating. The biscuits are baked first in a conventional oven at hot temperatures to brown the outside of each biscuit. Then, the biscuits are placed in a dielectric oven to cook the inside portions. Apparatus for use in a similar two-step process is described in U.S. Pat. No. 2,454,370 to Beaubien, which discloses conventional radiant heating means to toast the outside of the food product and high-frequency dielectric-field heating means to bake the inner portion of the food product. The Beaubien apparatus also provides a conveyor on which the food is moved through each oven.
The known processes which employ both conventional and dielectric heating operate so that the conventional oven is used first to set the structure and brown the surfaces of the food product and the dielectric heating apparatus is used next to speed up the final cooking of the food product. This combination of conventional and dielectric heating methods is employed in an attempt to gain precise control over the moisture endpoint of the final product, and shortens the total time required to dry to the desired moisture end point, thus enabling increased production rates and less floor space. Despite the decreased baking time required by this two-step process compared to completely baking a product in a conventional oven, the food products must still spend considerable time in the conventional oven before the products are ready to be heated in a dielectric oven.
There is a need in the art for a simple process for greatly reducing the drying time of hot plastic extruded food materials, and to decrease the floor space required for drying extruded food material. Dielectric drying of an extrudate would be advantageous over conventional drying which currently takes a great deal of manufacturing floor space. However, Applicant is unaware of any teachings in the art that dielectric drying of a hot plastic food material extrudate while still plastic would be useful in reducing the drying time and space required for drying.